This invention related generally to the electrically heated appliances such as electric comforters, and more particularly is directed to an improved electric comforter which can be economically manufactured and to the method of manufacturing the same.
Electric blankets have found wide acceptance as a topmost bed covering and generally comprise a two-ply woven cloth shell having channels in which are located a heating wire and safety thermostats connected thereto. Electric blankets of this type are disclosed in the following U.S. Pat. Nos.: 2,203,918 Mosberg June 11, 1940; 2,393,182 Newell Jan. 15, 1946; 2,722,951 Keily et al. Nov. 8, 1955; 2,961,526 Dykes Nov. 22, 1960.
Some electric blankets also have been constructed with shells comprising two plies of textile fabric united to each other at spaced points along parallel lines to form channels. A blanket shell which is made by stitching together two plies of fabric is shown in the Kerr U.S. Pat. No. 2,708,234 issued May 10, 1955. Other blanket shells have been formed by needle laminating two plies of fabric along spaced parallel bands as shown in the Rentz U.S. Pat. No. 3,431,611 issued Mar. 11, 1696.
Electric blankets serve as excellent, low cost bed covering for many people under ambient temperatures in the range of 60.degree. F. to 75.degree. F. However, bedroom temperatures well below 60.degree. F. are becoming increasingly common as people lower thermostat settings of their home heating systems at night to reduce energy costs. At temperatures below 60.degree. F., the value of the heating and insulating characteristics of the electric blanket begin to diminish for many users of electric blankets. As these characteristics diminish, users tend to place additional covering over the electric blanket to supplement its insulating characteristics. In doing so, the user is placing the electric blanket heating system in a "safety only" operating mode. The safety thermostats incorporated in a blanket to prevent overheating actually become the temperature control elements, and the control provided to control the blanket temperature becomes superfluous to blanket operation. When operating in this mode, the electric blanket temperature will stop rising when the temperature of the safety thermostat with the lowest calibrated temperature is exceeded. The electric blanket thus operates in an overheating mode which can be detrimental to the heating wire and safety thermostats. Misuse of this type is a frequent cause of electric blanket failure.
A quilted bedcovering such as a comforter provides better thermal insulation than does a blanket, and it has been recognized that an electrically heated comforter would be a desirable bedcovering. Examples of electric comforter construction which have been proposed in the past are disclosed by the following U.S. Pat. Nos.: 2,706,768 Kaplan April 19, 1955; 2,708,235 Kaplan May 10, 1955; 3,064,332 Kaplan Nov. 20, 1962; 3,102,186 Owers Aug. 27, 1963.
The electric comforter constructions shown in the Kaplan U.S. Pat. Nos. 2,706,768 and 2,708,235 are unsuitable for economical mass production. The comforter construction shown in the Kaplan U.S. Pat. No. 3,064,332 is better suited for mass production but has a serious shortcoming in that the heating wire is not positively positioned in the intermediate ply of insulating material. Besides being unsuitable for economical mass production, the electric comforter of the Owers U.S. Pat. No. 3,102,186 requires the use of thermoplastic insulating pads and apparently would not have the customary appearance and feel of the usual quilted comforter.
The continuous manufacture of comforters and other quilted fabrics with multi-needle stitching means is generally well known, and the use of such machines to produce an electric blanket shell is suggested in the above mentioned Kerr U.S. Pat. No. 2,708,234. Examples of such multi-needle stitching machines are shown in the following patents, the disclosures of which are incorporated herein by reference: 3,385,346 Schlegel May 28, 1968; 3,960,095 Story June 1, 1976; 4,006,697 Robertson Feb. 8, 1977.